This invention relates to the electrolytic production of hydrogen for use, particularly as a fuel for vehicles; and particularly to a system comprising an electrolytic cell for said production and a data network comprising data gathering, control and, optionally, storage.
Electrosynthesis is a method for production of chemical reaction(s) that is electrically driven by passage of an electric current, typically a direct current (DC), through an electrolyte between an anode electrode and a cathode electrode. An electrochemical cell is used for electrochemical reactions and comprises anode and cathode electrodes immersed in an electrolyte with the current passed between the electrodes from an external power source. The rate of production is proportional to the current flow in the absence of parasitic reactions. For example, in a liquid alkaline water electrolysis cell, the DC current is passed between the two electrodes in an aqueous electrolyte to split water, the reactant, into component product gases, namely, hydrogen and oxygen where the product gases evolve at the surfaces of the respective electrodes.
Water electrolysers have typically relied on pressure control systems to control the pressure between the two halves of an electrolysis cell to insure that the two gases, namely, oxygen and hydrogen produced in the electrolytic reaction are kept separate and do not mix.
One such pressure control system provides a water seal to equalize pressure in the two halves of the cell. This is the approach most often followed in xe2x80x9chome madexe2x80x9d electrolysers. Typically the water seal is a couple of inches deep and so the cell operates at a couple of inches of WC pressure above atmospheric.
An alternative system provides a membrane separator which can sustain a pressure difference between the two halves of the cell without gas mixing. The PEM (polymer electrolyte membrane) cell is the best example of this type of system. The PEM cell can sustain up to a 2500 psi pressure difference without a significant loss of gas purity.
A third is an active control system which senses pressure and controls the outflow of gases from the two cells. Control can be achieved in one of two ways:
by a mechanical system which relies on pressure regulators, such as a dome-loaded flow regulator to control pressure between the two cells which, for example, might employ the oxygen pressure as a reference pressure to regulate the pressure in the hydrogen half of the cell; and
by an electronic system which relies on measurement of the difference in gas pressure between the two cell to control the rates of gas outflow from the two sides of the cell so as to maintain a desired pressure difference of usually zero or with the hydrogen side slightly higher.
Typically, however, for very small commercial hydrogen generators (0.1 Nm3/h) PEM type electrolysis cells are favoured. Although the cost of the cell is far higher than for conventional alkaline electrolysers, these costs are more than offset by the controls needed for the conventional alkaline systems using mechanical or electronic actuators, and by the need for higher pressures and, hence, compression in electrolysers using a water seal pressure control system.
A hydrogen fuel replenishment system is operative in at least one North American city, wherein a fleet of public vehicles, namely, transit buses are refueled on a timely i.e. generally daily, basis from a storage tank(s) in a bus depot.
The hydrogen fuel tank on the bus is attached solely to the storage tank and the quantity of hydrogen to be furnished is calculated from the initial pressure and desired resultant pressure as read from pressure gauges on the bus or on the ground storage tank.
At the depot, hydrogen is provided to the storage tank(s) from on-site electrolyser(s) which maintain hydrogen pressure at a pre-determined value in the tank(s). Replenishment time is, generally, about 20-30 minutes.
However, the aforesaid hydrogen fuel replenishment system suffers from a significant number of disadvantages, as follows.
1. Modulation of the electrolyser cell bank is only by manual operation.
2. The cell bank is not easy to modulate, and accordingly, if the demand for hydrogen to be stored and for refueling vehicles in real time is lower than the cell supply rate, it is necessary to vent the hydrogen, generally to atmosphere.
3. The cell bank in real time cannot be modulated to optimize electricity usage at times of favourable, reduced electricity costs rates.
4. Each vehicle is filled by only manual operation.
5. Each vehicle is filled independently of other vehicles in the depot.
6. The nature of the filling operation is steady state with respect to the rate of filling from the cell bank. In filling a vehicle tank with hydrogen, the expansion and compression within the tank causes the gas temperature to rise and, hence, to yield a false value of a high pressure (full tank) if the rate of filling is too rapid. Upon subsequent cooling, the tank pressure falls and the tank requires a refill (top up) to achieve a truer desired pressure.
7. The use of storage tank(s) expands the necessary green space and foot print required for a filling station.
8. The use of storage tank(s) provides a potential safety risk requiring proper management.
There is, therefore, a need for a hydrogen fuel replenishment system which does not suffer from the aforesaid disadvantages.
It is an object of the present invention to provide a system for the in situ generation, on demand, of hydrogen gas for use particularly as a fuel for vehicles, requiring negligible on-site hydrogen storage.
It is a further object to provide a hydrogen fuel replenishment system which provides a practical user friendly control and activation interface.
It is a further object of the present invention to provide efficacious methods and apparatus for producing hydrogen at a minimum desired pressure.
Accordingly, in one aspect, the invention provides a hydrogen replenishment system for providing hydrogen to a hydrogen-receiving apparatus, said system comprising
(i) an electrolytic cell for providing source hydrogen;
(ii) a compressor means for providing outlet hydrogen at an outlet pressure;
(iii) means for feeding said source hydrogen to said compressor means;
(iv) means for feeding said outlet hydrogen to said hydrogen-receiving apparatus;
(v) central processing unit means for controlling said cell and said compressor; and
(vi) user activation means for operably activating said central processing unit means.
As used herein the term xe2x80x9ccellxe2x80x9d, xe2x80x9celectrochemical cellxe2x80x9d or xe2x80x9celectrolyserxe2x80x9d refers to a structure comprising at least one pair of electrodes including an anode and a cathode with each being suitably supported within an enclosure through which electrolyte is circulated and product is disengaged. The cell includes a separator assembly having appropriate means for sealing and mechanically supporting the separator within the enclosure. Multiple cells may be connected either in series or in parallel to form a cell stack and there is no limit on how may cells may be used to form a stack. In a stack the cells are connected in a similar manner, either in parallel or in series. A cell block is a unit which comprises one or more cell stacks and multiple cell blocks are connected together by an external bus bar. A functional electrolyser comprises one or more cells which are connected together either in parallel, in series, or a combination of both.
The electrolytic cell may comprise the compression means within its structure in that in one embodiment, hydrogen pressure is built up within the cell to the resultant desired user pressure and wherein the outlet hydrogen comprises source hydrogen.
The system and method according to the invention are of particular value for replenishing hydrogen fuel for a vehicle, such as a personal vehicle, truck, bus and the like.
Thus, the invention provides in a preferred aspect the system as hereinabove defined wherein said means (iv) comprises apparatus, preferably, vehicle attachment means attachable to the apparatus (vehicle) to provide the outlet hydrogen as fuel to the apparatus (vehicle). Accordingly, there is provided a system as hereinabove defined wherein means (iv) for feeding the outlet hydrogen to the hydrogen-receiving apparatus comprises conduit means and fitting engagement means adapted to be received in sealing engagement by said apparatus.
In an alternative embodiment, a system as hereinabove defined is provided wherein the conduit means and fitting engagement means comprises a plurality of conduits and fitting engagement members adapted to receive a plurality of the hydrogen-receiving apparatus.
The source hydrogen is preferably pumped through a conduit to the compressor.
The CPU comprises a system as hereinabove defined wherein the central processing unit comprises cell control means for activating the cell to provide the hydrogen source when the outlet pressure falls to a pre-selected value. The CPU preferably comprises the user activation means having data receiving means adapted to receive data from or by transfer means selected from the group consisting of an electronic data card, voice activation means, manually-operable selection and control means, radiated wavelength and electronic or electrical transfer. The CPU preferably comprises means for receiving and treating physical parameter data selected from the group consisting of temperature, pressures anolyte and catholyte liquid levels, bus continuity, KOH concentration, gas purities and process valves positions of the cell; and modulating and controlling the cell in consequence of said treatment of the cell data. It further comprises means for receiving and treating physical parameter data selected from the group consisting of temperature, inlet and outlet hydrogen pressures and valve status of the compressor means; and modulating and controlling the compressor means in consequence of the treatment of the compression means data. The CPU preferably comprises means for receiving and treating data selected from the group consisting of hydrogen demand of the hydrogen-receiving apparatus; and means for determining the amount, rate of delivery and duration of delivery of hydrogen to the apparatus in consequence of the hydrogen demand data. The CPU preferably comprises storage means for storing data selected from the hydrogen demand data, dates, times of day and night, and numbers of hydrogen-receiving apparatus.
Most preferably the CPU is in direct electrical or electronic communication with each of the cell, compressor and user activation means by means of electrical wires.
Thus, the control means and activation means provide for a practical user interface.
The system as hereinabove defined has also preferred utility wherein the conduit means and fitting engagement means comprises a plurality of conduits and fitting engagement members adapted to receive a plurality of the hydrogen-receiving apparatus, for example, a plurality of vehicles at a commercial, industrial or like outlet.
The introduction of the user activation means in combination with the CPU allows the advantageous exchange of data flow between the cell(s), compressor, vehicles(s) and sundry process control valves and conduits. This user interface allows for
1. defined demand, in real time, of the hydrogen needs for all vehicles, single or a plurality thereof, connected to the cell bank;
2. defined time to fill each vehicle(s) connected to the cell bank;
3. modulation of the cell bank to ensure the exact supply of hydrogen required by all vehicles over time;
4. modulation of the compressor in conjunction with the cell bank to ensure adequate supply of hydrogen to all vehicles in the absence of any storage tank(s), which reduces safety concerns;
5. modulation of the rate of filling of each vehicle via dynamic control of filling to provide a variable rate of filling to stabilize the temperature of the gas within the vehicle(s) and to ensure a correct real time value of pressure so as to assess a level of filling of the tank (i.e. half full, full, etc.) and a successful completion of the filling operation;
6. the achievement of aforesaid (1) to (5) with no manual user intervention;
7. the completion of data history of the operation of the cell bank and compressor is stored/recorded in run time hours to permit schedule maintenance, and
8. a complete data history of the storage of each vehicle to be stored/recorded.
The invention is of particular value in one embodiment when the apparatus comprises a cell to provide hydrogen at a desired minimum pressure; comprising an anolyte solution having an anolyte liquid level;
a catholyte solution having a catholyte liquid level;
oxygen generation means for generating oxygen at an oxygen pressure above said anolyte;
hydrogen generation means for generating hydrogen at a hydrogen pressure above said catholyte;
generated hydrogen outlet means;
and comprising pressure means for raising the oxygen pressure above the anolyte to effect a positive liquid level pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure through said outlet means.
This preferred aspect of the invention as hereinabove defined relies on creating a liquid level pressure differential between the catholyte liquid and the anolyte liquid levels by causing oxygen pressure build-up above the anolyte and fall in anolyte liquid level and a commensurate rise in catholyte level, while hydrogen is free to leave the cell until either (a) the anolyte level drops to a pre-selected level to trigger a control valve to prevent hydrogen release from the cell or (b) the catholyte level rises to similarly trigger the control value to similarly prevent hydrogen release from the cell. Subsequent build-up of hydrogen pressure above the catholyte reverses the respective liquid levels to effect opening of the control valves to provide hydrogen at the desired minimum pressure. Hydrogen pressure builds up under the closed release valve situation because two moles of hydrogen are produced for each mole of oxygen in the electrolytic process.
Accordingly in a further aspect, the invention provides a process for providing hydrogen at a desired minimum pressure from an electrolyser comprising
an anolyte solution having an anolyte liquid level;
a catholyte solution having a catholyte liquid level;
oxygen generated at an oxygen pressure above said anolyte;
hydrogen generated at a hydrogen pressure above said catholyte for passage through hydrogen outlet means; the process comprising raising the oxygen pressure above the anolyte to effect a liquid levels pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure.
In a further aspect, the invention provides an electrolyser for providing hydrogen at a desired minimum pressure comprising
an anolyte solution having an anolyte liquid level;
a catholyte solution having a catholyte liquid level;
oxygen generation means for generating oxygen at an oxygen pressure above said anolyte;
hydrogen generation means for generating hydrogen at a hydrogen pressure above said catholyte;
generated hydrogen outlet means; and comprising pressure means for raising the oxygen pressure above the anolyte to effect a liquid level pressure differential between said catholyte liquid level and said anolyte liquid level to a pre-selected value to effect closure of said hydrogen outlet means and an increase in the hydrogen pressure to a value to effect opening of said hydrogen outlet means to provide hydrogen at said desired minimum pressure through said outlet means.